Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756846Ab3CSDS2 (ORCPT ); Mon, 18 Mar 2013 23:18:28 -0400 Received: from mail.linux-iscsi.org ([67.23.28.174]:57824 "EHLO linux-iscsi.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751001Ab3CSDS0 (ORCPT ); Mon, 18 Mar 2013 23:18:26 -0400 Subject: Re: [ 04/21] target/pscsi: Fix page increment From: "Nicholas A. Bellinger" To: Ben Hutchings Cc: Asias He , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Greg Kroah-Hartman , target-devel In-Reply-To: <1363655903.3937.350.camel@deadeye.wl.decadent.org.uk> References: <20130312223245.109098379@linuxfoundation.org> <20130312223245.664885170@linuxfoundation.org> <1363399822.3937.161.camel@deadeye.wl.decadent.org.uk> <20130318053519.GE6232@hj.localdomain> <1363640434.3156.36.camel@haakon2.linux-iscsi.org> <1363649447.3937.348.camel@deadeye.wl.decadent.org.uk> <20130319005659.GB15879@hj.localdomain> <1363655903.3937.350.camel@deadeye.wl.decadent.org.uk> Content-Type: text/plain; charset="UTF-8" Date: Mon, 18 Mar 2013 20:18:23 -0700 Message-ID: <1363663103.3156.158.camel@haakon2.linux-iscsi.org> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4243 Lines: 105 On Tue, 2013-03-19 at 01:18 +0000, Ben Hutchings wrote: > On Tue, 2013-03-19 at 08:56 +0800, Asias He wrote: > > On Mon, Mar 18, 2013 at 11:30:47PM +0000, Ben Hutchings wrote: > > > On Mon, 2013-03-18 at 14:00 -0700, Nicholas A. Bellinger wrote: > > > > On Mon, 2013-03-18 at 13:35 +0800, Asias He wrote: > > > > > On Sat, Mar 16, 2013 at 02:10:22AM +0000, Ben Hutchings wrote: > > > > > > On Tue, 2013-03-12 at 15:44 -0700, Greg Kroah-Hartman wrote: > > > > > > > 3.0-stable review patch. If anyone has any objections, please let me know. > > > > > > > > > > > > > > ------------------ > > > > > > > > > > > > > > From: Asias He > > > > > > > > > > > > > > commit 472b72f2db7831d7dbe22ffdff4adee3bd49b05d upstream. > > > > > > > > > > > > > > The page++ is wrong. It makes bio_add_pc_page() pointing to a wrong page > > > > > > > address if the 'while (len > 0 && data_len > 0) { ... }' loop is > > > > > > > executed more than one once. > > > > > > > > > > > > > > Signed-off-by: Asias He > > > > > > > Signed-off-by: Nicholas Bellinger > > > > > > > Signed-off-by: Greg Kroah-Hartman > > > > > > > > > > > > > > --- > > > > > > > drivers/target/target_core_pscsi.c | 1 - > > > > > > > 1 file changed, 1 deletion(-) > > > > > > > > > > > > > > --- a/drivers/target/target_core_pscsi.c > > > > > > > +++ b/drivers/target/target_core_pscsi.c > > > > > > > @@ -1210,7 +1210,6 @@ static int __pscsi_map_task_SG( > > > > > > > bio = NULL; > > > > > > > } > > > > > > > > > > > > > > - page++; > > > > > > > len -= bytes; > > > > > > > data_len -= bytes; > > > > > > > off = 0; > > > > > > > > > > > > So in case a fragment crosses a page boundary, we wrap around to the > > > > > > beginning of the same page? That doesn't look right. > > > > > > > > > > If the fragment crosses a page boundary, what is the correct page > > > > > for it? > > > > > > > > > > Nicholas, can we assume sg->length + sg->offset should be less than PAGE_SIZE here? > > > > > > > > > > > > > sg->length + sg->offset can be less than or equal to PAGE_SIZE here. > > > > > > > > For everything other than tcm_loop + tcm_vhost using externally > > > > allocated SGLs, we can expect fragments to never cross the page > > > > boundary. > > > > > > > > For tcm_loop + tcm_vhost, there are a few special cases with control CDB > > > > paylaods (usually going through scsi-generic) where we can have a non > > > > zero sg->offset, but at least in the cases I've seen this is still not > > > > using SGL elements that exceed PAGE_SIZE. > > > > > > > > So, I think this logic is OK for SGLs that cross page boundries, given > > > > that it's done outside of the inner loop where *page is set during each > > > > for_each_sg(). > > > > > > The page is set using sg_page() in the outer loop and was then > > > incremented in the inner loop. > > > > > > for_each_sg(sgl, sg, sgl_nents, i) { > > > page = sg_page(sg); > > > off = sg->offset; > > > len = sg->length; > > > > > > while (len > 0 && data_len > 0) { > > > bytes = min_t(unsigned int, len, PAGE_SIZE - off); > > > bytes = min(bytes, data_len); > > > ... > > > /* page++; */ > > > len -= bytes; > > > data_len -= bytes; > > > off = 0; > > > } > > > } > > > > > > The inner loop is apparently meant to iterate over pages of a segment, > > > but is now just wrapping around a single page. > > > > Yes, but we never loop more than once in the inner loop. > > If you're sure of that, then: > > > So, how about > > 1) fail on sg->offset + sg->length > PAGE_SIZE (we can not find a > > proper page address in this case) > > 2) remove the inner while loop, run the code was in the loop only once. > > this is fine, but then I don't understand why you sent a no-op change to > stable in the first place. > It's my fault for mis-understanding this patch, and putting this into the queue as a stable bug-fix. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/